The proposed project is a systematic biochemical investigation of the structure and function of animal cell surfaces. Particular attention will be devoted to examining the surface components of mouse L cells. For example, lactoperoxidase-catalyzed iodination studies will be carried out with whole L cells and with "inside-out" membrane vesicles prepared from L cells to identify membrane proteins exposed on the outer and on the inner membrane surfaces, respectively. Complementary studies, also involving the use of inside-out vesicles, will be performed to determine whether the phospholipids phosphatidylethanolamine and phosphatidylserine are found preferentially on either the inner or on the outer lipid leaflet. Extensive studies will also be carried out on the biological properties of one particular cell surface glycoprotein species, a concanavalin A (Con A) receptor recently isolated from L cells. An antiserum will be prepared to the Con A receptor and used to determine whether other cell types have surface glycoproteins antigenically similar to the L cell Con A receptor and whether the receptor is free to move laterally in the plane of the plasma membrane. Other studies will be devoted to isolating L cell mutants lacking the Con A receptor and to clarifying the role of the Con A receptor in the cytotoxicity of Con A.